Substrate-less stackable package with wire-bond interconnect

ABSTRACT

A method for making a microelectronic unit includes forming a plurality of wire bonds on a first surface in the form of a conductive bonding surface of a structure comprising a patternable metallic element. The wire bonds are formed having bases joined to the first surface and end surfaces remote from the first surface. The wire bonds have edge surfaces extending between the bases and the end surfaces. The method also includes forming a dielectric encapsulation layer over a portion of the first surface of the conductive layer and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by end surfaces or portions of the edge surfaces that are unconvered by the encapsulation layer. The metallic element is patterned to form first conductive elements beneath the wire bonds and insulated from one another by portions of the encapsulation layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/486,867, filed Sep. 15, 2014, which is a divisional of U.S.patent application Ser. No. 13/477,532, filed May 22, 2012, (now U.S.Pat. No. 8,835,228), the disclosure of each of which is incorporatedherein by reference in its entirety for all purposes consistentherewith.

BACKGROUND OF THE INVENTION

Microelectronic devices such as semiconductor chips typically requiremany input and output connections to other electronic components. Theinput and output contacts of a semiconductor chip or other comparabledevice are generally disposed in grid-like patterns that substantiallycover a surface of the device (commonly referred to as an “area array”)or in elongated rows which may extend parallel to and adjacent each edgeof the device's front surface, or in the center of the front surface.Typically, devices such as chips must be physically mounted on asubstrate such as a printed circuit board, and the contacts of thedevice must be electrically connected to electrically conductivefeatures of the circuit board.

Semiconductor chips are commonly provided in packages that facilitatehandling of the chip during manufacture and during mounting of the chipon an external substrate such as a circuit board or other circuit panel.For example, many semiconductor chips are provided in packages suitablefor surface mounting. Numerous packages of this general type have beenproposed for various applications. Most commonly, such packages includea dielectric element, commonly referred to as a “chip carrier” withterminals formed as plated or etched metallic structures on thedielectric. These terminals typically are connected to the contacts ofthe chip itself by features such as thin traces extending along the chipcarrier itself and by fine leads or wires extending between the contactsof the chip and the terminals or traces. In a surface mountingoperation, the package is placed onto a circuit board so that eachterminal on the package is aligned with a corresponding contact pad onthe circuit board. Solder or other bonding material is provided betweenthe terminals and the contact pads. The package can be permanentlybonded in place by heating the assembly so as to melt or “reflow” thesolder or otherwise activate the bonding material.

Many packages include solder masses in the form of solder balls,typically about 0.1 mm and about 0.8 mm (5 and 30 mils) in diameter,attached to the terminals of the package. A package having an array ofsolder balls projecting from its bottom surface is commonly referred toas a ball grid array or “BGA” package. Other packages, referred to asland grid array or “LGA” packages are secured to the substrate by thinlayers or lands formed from solder. Packages of this type can be quitecompact. Certain packages, commonly referred to as “chip scalepackages,” occupy an area of the circuit board equal to, or onlyslightly larger than, the area of the device incorporated in thepackage. This is advantageous in that it reduces the overall size of theassembly and permits the use of short interconnections between variousdevices on the substrate, which in turn limits signal propagation timebetween devices and thus facilitates operation of the assembly at highspeeds.

Packaged semiconductor chips are often provided in “stacked”arrangements, wherein one package is provided, for example, on a circuitboard, and another package is mounted on top of the first package. Thesearrangements can allow a number of different chips to be mounted withina single footprint on a circuit board and can further facilitatehigh-speed operation by providing a short interconnection betweenpackages. Often, this interconnect distance is only slightly larger thanthe thickness of the chip itself. For interconnection to be achievedwithin a stack of chip packages, it is necessary to provide structuresfor mechanical and electrical connection on both sides of each package(except for the topmost package). This has been done, for example, byproviding contact pads or lands on both sides of the substrate to whichthe chip is mounted, the pads being connected through the substrate byconductive vias or the like. Solder balls or the like have been used tobridge the gap between the contacts on the top of a lower substrate tothe contacts on the bottom of the next higher substrate. The solderballs must be higher than the height of the chip in order to connect thecontacts. Examples of stacked chip arrangements and interconnectstructures are provided in U.S. Patent App. Pub. No. 2010/0232129 (“the'129 Publication”), the disclosure of which is incorporated by referenceherein in its entirety.

Despite all of the above-described advances in the art, still furtherimprovements in making and testing microelectronic packages would bedesirable.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present disclosure relates to a method for making amicroelectronic unit. The method includes forming a plurality of wirebonds on a first surface in the form of a conductive bonding surface ofa structure comprising a patternable metallic element. The wire bondsare formed having bases joined to the first surface and end surfacesremote from the bases and remote from the first surface. The wire bondsfurther have edge surfaces extending between the bases and the endsurfaces. The method also includes forming a dielectric encapsulationlayer over at least a portion of the first surface of the conductivelayer and over portions of the wire bonds such that unencapsulatedportions of the wire bonds are defined by at least one of the endsurface or a portion of the edge surface thereof that is uncovered bythe encapsulation layer. Then, the metallic element is selectivelypatterned to form first conductive elements insulated from one anotherby at least portions of the encapsulation layer. At least some of thewire bonds are disposed atop the first conductive elements.

A microelectronic element can be included in the structure andelectrically connected with the conductive layer when the step ofremoving portions of the conductive layer is performed. The step offorming the dielectric encapsulation layer can be carried out with themicroelectronic element electrically connected with the conductive layerand such that the encapsulation layer at least partially covers at leastone surface thereof. At least some of the first conductive elements canbe electrically connected between respective ones of the wire bonds andthe microelectronic element.

An example of the method can further include the step of forming aredistribution layer over the second surface of the encapsulation layer.The redistribution layer can include conductive contacts displaced in atleast one lateral direction from the unexposed portions of the wirebonds.

At least some of the wire bonds can be formed such that the end surfacesthereof are displaced in one or more lateral directions from the basesthereof. In an example, the bases of the wire bonds can be arranged in afirst pattern having a first minimum pitch and the unencapsulatedportions of the wire bonds can be arranged in a pattern having a secondminimum pitch that is greater than the first minimum pitch.Alternatively, the bases can be arranged in a first pattern having afirst minimum pitch and the unencapsulated portions of the wire bondscan be arranged in a pattern having a second minimum pitch that is lessthan the first minimum pitch.

The method can further include forming second conductive elementsoverlying the second surface of the dielectric layer. At least some ofthe second conductive elements can be connected with respective ones ofat least some of the unencapsulated portions of the wire bonds.

The step of selectively removing portions of the conductive layer caninclude forming at least some first conductive elements as contact padsto which bases of wire bonds that are not electrically connected withother elements of the unit are electrically connected.

The method can further include the step of thinning the unit by one ofgrinding or polishing. In an example, the encapsulation layer can beformed having an initial thickness such that the end surfaces of thewire bonds are substantially covered, and the step of thinning the unitcan include removing a portion of the encapsulation layer such that theend surfaces become unencapsulated by the encapsulation layer.

The step of forming the encapsulation layer can include dispensing anencapsulant onto the first surface of the conductive layer and at leastedge surfaces of the wire bonds. Further, the step of forming theencapsulation layer can include molding an encapsulant in contact withthe conductive layer, at least edge surfaces of the wire bonds, and atleast one surface of the microelectronic element.

The method can further include removing a carrier from a surface of theconductive layer opposite the wire bonds prior to performing the step ofselectively removing portions of the conductive layer.

In an embodiment, the conductive layer can have a thickness of less than20 microns.

Another aspect of the present disclosure relates to a method for makinga microelectronic package. The method can include forming a plurality ofwire bonds on a first surface of a conductive layer of an in processunit. The in-process unit has at least one microelectronic elementjoined thereto that is electrically connected with portions thereof. Thewire bonds are formed having bases joined to the first surface and endsurfaces remote from the bases and remote from the first surface. Thewire bonds further have edge surfaces extending between the bases andthe end surfaces. The method also includes forming a dielectricencapsulation layer over at least a portion of the first surface of theconductive layer, over at least a portion of the at least onemicroelectronic element, and over portions of the wire bonds such thatunencapsulated portions of the wire bonds are defined by at least one ofthe end surface or a portion of the edge surface thereof that isuncovered by the encapsulation layer. Portions of the conductive layerare selectively removed to form first conductive elements thereof. Atleast some of the first conductive elements are electrically connectedwith at least some of the wire bonds, and at least some of the firstconductive elements include at least some of the portions of theconductive layer with which the microelectronic element is electricallyconnected.

Another aspect of the present disclosure relates to a method for makinga microelectronic unit. The method includes forming a plurality of wirebonds on a first surface that is a conductive bonding surface of astructure comprising a patternable metallic element. The wire bonds havebases joined to the first surface and end surfaces remote from the basesand remote from the first surface. The wire bonds further have edgesurfaces extending between the bases and the end surfaces. When formingthe wire bonds, the conductive layer includes a plurality of regionsattached to one another at at least some edges thereof. The method alsoincludes forming a dielectric encapsulation layer over at least aportion of the first surface of the conductive layer and over portionsof the wire bonds, such that unencapsulated portions of the wire bondsare defined by at least one of the end surface or a portion of the edgesurface thereof that is uncovered by the encapsulation layer, whereinwhen performing the step of selectively removing portions of theencapsulation layer, a plurality of microelectronic elements are joinedto the conductive layer, in the form of an in-process unit having atleast one microelectronic element electrically connected with each of atleast some of the regions of the conductive layer. The metallic elementis then selectively patterned to form first conductive elementsinsulated from one another by at least portions of the encapsulationlayer. At least some of the wire bonds are disposed atop the firstconductive elements. The in-process unit is then severed into aplurality of microelectronic units, each including the first conductiveelements of a region of the conductive layer and the at least onemicroelectronic element electrically connected therewith.

Another aspect of the present disclosure relates to a method for makinga microelectronic assembly. The method includes making a firstmicroelectronic package, including forming a plurality of wire bonds ona first surface of a conductive layer of an in process unit. Thein-process unit has at least one microelectronic element joined theretoand electrically connected with portions thereof. The wire bonds areformed having bases joined to the first surface and end surfaces remotefrom the bases and remote from the first surface. The wire bonds furtherhave edge surfaces extending between the bases and the end surfaces.Forming the first microelectronic package also includes forming adielectric encapsulation layer over at least a portion of the firstsurface of the conductive layer, over at least a portion of the at leastone microelectronic element, and over portions of the wire bonds suchthat unencapsulated portions of the wire bonds are defined by at leastone of the end surface or a portion of the edge surface thereof that isuncovered by the encapsulation layer. Portions of the conductive layerare then selectively removed to form first conductive elements thereof.At least some of the first conductive elements are electricallyconnected with at least some of the wire bonds and at least some of thefirst conductive elements include at least some of the portions of theconductive layer with which the microelectronic element is electricallyconnected. The method also includes joining the first microelectronicpackage with a second microelectronic package overlying the secondsurface of the encapsulation layer of the first package. The secondmicroelectronic package includes a plurality of contacts exposed at afirst surface thereof. Joining the first microelectronic package withthe second microelectronic package includes electrically connecting theunencapsulated portions of the wire bonds of the first microelectronicpackage with the contacts of the second microelectronic package.

Another aspect of the present disclosure relates to a microelectronicpackage including at least one microelectronic element. The packagefurther includes first electrically conductive elements includingterminals exposed at a mounting surface of the package. At least some ofthe first conductive elements are electrically connected to the at leastone microelectronic element through vias integrally formed with thefirst conductive elements. The package further includes wire bondshaving bases joined to respective ones of the conductive elements andadjacent the first surface of the dielectric encapsulation layer and endsurfaces remote from the bases. Each wire bond defines an edge surfaceextending between the base and the end surface thereof. The package alsoincludes a dielectric encapsulation layer having a first surface and asecond surface remote from the first surface. At least a portion of thefirst surface is exposed at the mounting surface of the package. Thedielectric encapsulation layer fills spaces between the wire bonds suchthat the wire bonds are separated from one another by the encapsulationlayer. Unencapsulated portions of the wire bonds are defined by at leastportions of the end surfaces of the wire bonds that are uncovered by theencapsulation layer at the second surface thereof.

At least some of the unencapsulated portions of the wire bonds can bedisplaced in at least one lateral direction from the respective basesthereof.

The package can further include a second microelectronic element. In anexample the first microelectronic element can include contacts exposedat a front face thereof that are disposed toward the first surface ofthe dielectric layer, and the second microelectronic element can includecontacts exposed at a front face thereof that is disposed toward thesecond surface of the dielectric layer. In such an example, the packagecan further include second conductive elements exposed at the secondsurface of the encapsulation layer. At least some of the secondconductive elements can be connected between respective ones of thecontacts of the second microelectronic element and respective ones ofthe unencapsulated wire bond portions. The first and secondmicroelectronic elements can be electrically connected by at least onewire bond that is electrically connected with at least one contact ofthe first microelectronic element and at least one contact of the secondmicroelectronic element. Alternatively, the second microelectronicelement can be connected with one of the second conductive elements by awire bond joined between one of the contacts of the secondmicroelectronic element and a respective one of the secondmicroelectronic elements. In another example, the first and secondmicroelectronic elements can be electrically connected by a wire bondjoined to a contact of the second microelectronic element and arespective one of the conductive elements exposed at the first surfaceof the encapsulation layer.

A microelectronic assembly can include a first microelectronic packageas described above and a second microelectronic package that includes amicroelectronic element and terminals exposed at a surface of the secondmicroelectronic package. The terminals can be electrically connectedwith the microelectronic element. Further, the second microelectronicpackage can overlie the first microelectronic package and can be bondedthereto with the terminals thereof electrically connected to at leastsome of the unencapsulated portions of the wire bonds of the firstmicroelectronic package.

A system can include a microelectronic package, as described above andone or more electronic components.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will be now described withreference to the appended drawings. It is appreciated that thesedrawings depict only some embodiments of the invention and are thereforenot to be considered limiting of its scope.

FIG. 1 shows a top schematic view of an in-process unit that can beprocessed to form a microelectronic package by steps according to amethod of the present disclosure;

FIG. 2 shows a side elevation of the in-process unit of FIG. 1;

FIG. 3 shows a top view of the in-process unit of FIG. 1 in a furtherprocess step of the method;

FIG. 4 shows a side elevation view of the in-process unit of FIG. 3;

FIG. 5 shows a detail view of a portion of the in-process unit of FIG. 4as indicated by area or detail A;

FIG. 6 shows a top view of the in-process unit of FIG. 1 in a furtherprocess step of the method;

FIG. 7 shows a side elevation view of the in-process unit of FIG. 6;

FIG. 8 shows a detail view of a portion of the in-process unit of FIG. 7as indicated by area B or detail;

FIG. 9 shows a side elevation view of a microelectronic package that canresult from the method;

FIG. 10 shows a detail view of the package of FIG. 9 as indicted by areaor detail C;

FIG. 11 shows the detail view of FIG. 10 after a further optionalprocess step of the method;

FIG. 12 shows a side view of the package of Fig. in a further optionalprocess step of the method;

FIG. 13 shows a detail view of a portion of the package of FIG. 11 asindicated by area or detail D;

FIG. 14 shows an alternative in-process unit that can be processed toform a microelectronic package by steps according to variation of amethod of the present disclosure;

FIG. 15 shows a detail view of a portion of the in-process unit of FIG.13 as indicated by area E;

FIG. 16 shows a side elevation view of a microelectronic package thatcan result from the method variation;

FIG. 17 shows a detail view of a portion of the package of FIG. 15 afteran optional process step of another method variation;

FIG. 18 shows an alternative microelectronic package;

FIG. 19 shows a detail view of a portion of the package of FIG. 18 asindicated by area F;

FIG. 20 shows a further alternative microelectronic package;

FIG. 21 shows a detail view of a portion of the package of FIG. 20 asindicated by area G;

FIG. 22 shows a further alternative microelectronic package;

FIG. 23 shows a further alternative microelectronic package; and

FIG. 24 shows an example of a microelectronic assembly that can includeone or more packages according to various embodiments shown herein.

FIG. 25 depicts an example of a system which may include a packageaccording to an implementation described herein.

DETAILED DESCRIPTION

Turning now to the figures, where similar numeric references are used toindicate similar features, there is shown in FIG. 9 a microelectronicunit or package 10 according to an embodiment of the disclosure, forwhich FIGS. 1-8 show various stages of formation of the microelectronicpackage according to a method in another embodiment of the disclosure.The embodiment of FIG. 9 is a microelectronic package 10 in the form ofa packaged microelectronic element such as a semiconductor chip assemblythat is used in computer or other electronic applications.

The microelectronic package 10 of FIG. 9 includes a microelectronicelement 22. The microelectronic package 10 can be embedded within anencapsulation layer 42 or may be contacted by the encapsulation layer atone or more surfaces thereof, e.g., a front or rear surface or an edgesurface extending between the front and rear surfaces. The encapsulationlayer 42 has a thickness extending from a first surface 43 or 45 to asecond surface 44. The first and second surfaces can be at leastpartially exposed at respective first and second mounting surfaces 11and 12 of the packages 10. Such a thickness can be at least equal to athickness of the microelectronic element 22, itself. As seen in FIG. 10,encapsulation layer 42 can further extend outwardly from themicroelectronic element 22 in lateral directions, as also shown in theplan-view of FIG. 6. A plurality of wire bonds 32 are also embeddedwithin encapsulation layer and extend between end surfaces 35 and 38that are respectively uncovered by the encapsulation layer and which maybe flush (e.g., co-planar) with surfaces 43 or 45 and 44. For purposesof this discussion, the first surface 43 or 45 may be described as beingpositioned opposite or remote from second surface 44. Such adescription, as well as any other description of the relative positionof elements used herein that refers to a vertical or horizontal positionof such elements is made for illustrative purposes only to correspondwith the position of the elements within the Figures, and is notlimiting.

Microelectronic element 22 can be a semiconductor chip or anothercomparable device having a plurality of active or passive circuitelements therein or both active and passive circuit elements which maybe in the form of an integrated passives on-chip (“IPOC”), among others.In the embodiment of FIG. 10, microelectronic element 22 has at leastportions of edge and rear surfaces contacted (e.g., covered by)encapsulation layer 42. The microelectronic element 22 may be positionedsuch that its contacts 24 are adjacent the first mounting surface 11 ofthe package. Further, in such an arrangement, contacts 24 are connectedwith conductive elements that extend along first surface 43 or 45 ofencapsulation layer 42 to electrically connect with wire bonds 32 at endsurfaces 35, thereof, which can be defined by bases 34 of the respectivewire bonds 32. Such bases 34 can be an artifact of the process used toform wire bonds 32, and can be in the shape of such bases 34 as formedby ball bonding, as shown, or by wedge bonding, stitch bonding or thelike. In other embodiments, such as that shown in FIG. 16, bases can bepartially or fully removed during fabrication, such as by a thinningprocess of grinding, lapping, polishing, or other suitable technique.Such thinning or other process can also reduce the height of the wirebonds 132 such that end surfaces 135 are defined as extremities of thewire bonds 132 that were above the bases. In an embodiment, themicroelectronic contacts 24 can be electrically connected withconductive elements 28 by conductive (e.g., metalized) vias 25 thatinclude vias deposited onto the contacts 24 of the microelectronicelement such as by plating, sputtering, or vapor deposition of one ormore metals, such as one or more of copper, nickel, chromium, aluminum,gold, titanium, tungsten, cobalt, or one or more alloys thereof, withoutlimitation. In one example, conductive elements can be formed bydepositing a liquid conductive matrix material having metallic andnon-metallic components, and thereafter curing the deposited conductivematrix material. For example, a conductive matrix material can bedeposited and used such as described in commonly owned U.S. patentapplication Ser. No. 13/158,797, the disclosure of which is incorporatedby reference herein.

Conductive elements 28 can include respective “contacts” or “pads” thatcan be exposed at the second surface of encapsulation layer 42. As usedin the present description, when an electrically conductive element isdescribed as being “exposed at” the surface of another element havingdielectric structure, it indicates that the electrically conductivestructure is available for contact with a theoretical point moving in adirection perpendicular to the surface of the dielectric structuretoward the surface of the dielectric structure from outside thedielectric structure. Thus, a terminal or other conductive structurethat is exposed at a surface of a dielectric structure may project fromsuch surface; may be flush with such surface; or may be recessedrelative to such surface and exposed through a hole or depression in thedielectric. In one example, the conductive elements 28 can be flat, thinelements that are exposed at first surface 43 of encapsulation layer 42.Conductive elements 28 can have any suitable shape and in some cases canbe circular. Conductive elements 28 may be electrically interconnectedwith one another, to microelectronic element 22, or both, by traces 31.Conductive elements 28 can also be formed along front surface 20 ofmicroelectronic element 22.

As shown in FIGS. 12 and 13, additional conductive elements 28 can beexposed at a second surface 44 of encapsulation layer 42. Suchconductive elements 28 can overlie and electrically connect with endsurfaces 38 of wire bonds 32. In other variations, such conductiveelements can include pads that are displaced in at least one lateraldirection along surface 44 from a corresponding wire bond, to which theycan be connected at an end surface thereof by a trace 31.

Wire bonds 32 can be joined to at least some of the conductive elements28, such as on the faces thereof. Wire bonds 32 can be joined at a base34 thereof to the conductive elements 28 and can extend to an end 36remote, i.e. opposite, from the respective bases 34 and from firstsurface 43. The ends 36 of wire bonds 32 can be characterized as being“free” in that they are not electrically connected or otherwise joinedto microelectronic element 22 or any other conductive features withinmicroelectronic package 10 that are, in turn, connected tomicroelectronic element 22. In other words, free ends 36 are availablefor electronic connection, either directly or indirectly as through aconductive element 28 or other features discussed herein, to aconductive feature external to package 10. The fact that ends 36 areheld in a predetermined position by, for example, encapsulant layer 42or otherwise joined or electrically connected to another conductivefeature does not mean that they are not “free” as described herein, solong as any such feature is not electrically connected tomicroelectronic element 22. Conversely, bases 34 may not be free as theycan be either directly or indirectly electrically connected tomicroelectronic element 22, as described herein. As shown in FIG. 10,bases 34 can be rounded in shape, extending outward from an edge surface37 of wire bond 32 defined between base 34 and end 36. The particularsize and shape of base 34 can vary according to the type of materialused to form wire bond 32, the desired strength of the connectionbetween wire bond 32 and conductive element 28, or the particularprocess used to form wire bond 32. Exemplary methods for making wirebonds 32 are described in U.S. Pat. No. 7,391,121 to Otremba, in U.S.Pat. App. Pub. No. 2005/0095835 (describing a wedge-bonding procedurethat can be considered a form of wire bonding), and in commonly-assignedU.S. patent application Ser. Nos. 13/462,158; 13/404,408; 13/405,108;13/405,125; and 13/404,458, the disclosures of which are incorporatedherein by reference in their entireties.

Wire bonds 32 are formed by bonding a metal wire made of copper, gold,nickel, solder, aluminum, or metal alloy, among others, at a surfacethereof and performing one or more other steps so as to form a wire bondhaving a base and an unencapsulated surface remote, e.g., opposite,therefrom with a length of the wire extending therebetween.Additionally, wire bonds 32 can be made from combinations of materials,such as from a core of a conductive material, such as copper oraluminum, for example, with a coating applied over the core. The coatingcan be of a second conductive material, such as aluminum, nickel,platinum, or palladium, among others. Alternatively, the coating can beof an insulating material, such as an insulating jacket. In anembodiment, the wire used to form wire bonds 32 can have a thickness,i.e., in a dimension transverse to the wire's length, of between about15 μm and 150 μm. In general, wire bonds 32 can be formed on a metalbonding surface, i.e. a first metal bonding surface of a structure usinga wire bond tool. In other embodiments, including those in which wedgebonding is used, such as described below, wire bonds 32 can have athickness of up to about 500 μm. A leading end of a wire segment isheated and pressed against the receiving surface to which the wiresegment bonds, typically forming a ball or ball-like base 34 joined tothe surface of the conductive element 28. The desired length of the wiresegment to form the wire bond is drawn out of the bonding tool, whichcan then sever or cut the wire bond at the desired length. Wedgebonding, which can be used to form wire bonds of aluminum, for example,is a process in which the heated portion of the wire is dragged acrossthe receiving surface to form a wedge that lies generally parallel tothe surface. The wedge-bonded wire bond can then be bent upward, ifnecessary, and extended to the desired length or position beforecutting. In a particular embodiment, the wire used to form a wire bondcan be cylindrical in cross-section. Otherwise, the wire fed from thetool to form a wire bond or wedge-bonded wire bond may have a polygonalcross-section such as rectangular or trapezoidal, for example.

The free ends 36 of wire bonds 32 can define respective end surfaces 38.End surface 38 can form at least a part of a contact in a pattern suchas a grid or an array formed by respective end surfaces 38 of aplurality of wire bonds 32. FIGS. 6 and 7 show an exemplary pattern forsuch an array of contacts formed by end surfaces 38. Such an array canbe formed in an area array configuration, variations of which could beimplemented using the structures described herein. In a variation ofthat shown, there need not be end surfaces of a wire bond at everyposition of the grid or array pattern in FIG. 6. Such an array can beused to electrically and mechanically connect the microelectronicpackage 10 to another microelectronic structure, such as to a printedcircuit board (“PCB”), or to other packaged microelectronic elements, anexample of which is shown in FIG. 24. In such a stacked arrangement,wire bonds 32 and conductive elements 28 can carry multiple electronicsignals therethrough, each having a different signal potential to allowfor different signals to be processed by different microelectronicelements in a single stack. The grid or array pattern in which endsurfaces 38 are disposed at certain positions that can be disposed atpositions thereof that are the same as or different than the grid orarray pattern in which bases 34 are disposed. In the example shown inFIG. 9, where wire bonds 32 are generally vertically arranged, sucharrays may be identical. In other arrangements, such as that shown inFIG. 23 can include wire bonds 532 that are angled 546 with respect tosurface 544 of encapsulation layer 542 such that the array of endsurfaces 38 has a greater pitch than that of bases 34. An inverse ofsuch an arrangement is also possible. Further, as discussed above,conductive elements 28 can be laterally displaced from end surfaces 35or 38 to which they are electrically connected by traces 31. Thisarrangement can also provide for different pitches over surfaces 544 and545 or other different arrangements of contacts.

As shown in FIG. 24 such a package 10 can be arranged in a stack withother similar packages or the like. While FIG. 24 shows two suchmicroelectronic packages 10A, 10B, three, four or even more can bearranged in such a stack, which can also be assembled with a circuitpanel 90 with solder masses 52 joining conductive elements 28 to panelcontacts 92. Solder masses 52 can also be used to interconnect themicroelectronic assemblies in such a stack, such as by electronicallyand mechanically attaching end surfaces 38 to conductive elements 28 orconnecting conductive elements 28 to other conductive elements 28.

Encapsulation layer 42 serves to protect the other elements withinmicroelectronic package 10, particularly wire bonds 32. This allows fora more robust structure that is less likely to be damaged by testingthereof or during transportation or assembly to other microelectronicstructures. Encapsulation layer 42 can be formed from a dielectricmaterial with insulating properties such as that described in U.S.Patent App. Pub. No. 2010/0232129, which is incorporated by referenceherein in its entirety.

As discussed above, FIG. 23 shows an embodiment of microelectronicassembly 510 having wire bonds 532 with ends 536 that are not positioneddirectly above the respective bases 34 thereof. That is, consideringfirst surface 544 of assembly 510 as extending in two lateraldirections, so as to substantially define a plane, end 536 or at leastone of the wire bonds 532 is displaced in at least one of these lateraldirections from a corresponding lateral position of base 34. As shown inFIG. 23, wire bonds 532 can be substantially straight along thelongitudinal axis thereof, as in the embodiment of FIG. 9, with thelongitudinal axis being angled at an angle 546 with respect to a firstsurface 544 of encapsulation layer 542. Although the cross-sectionalview of FIG. 23 only shows the angle 546 through a first planeperpendicular to first surface 544, wire bond 532 can also be angledwith respect to second surface 545 in another plane perpendicular toboth that first plane and to second surface 545. Such an angle can besubstantially equal to or different than angle 546. That is thedisplacement of end 536 relative to base 34 can be in two lateraldirections and can be by the same or a different distance in each ofthose directions.

In an embodiment, various ones of wire bonds 532 can be displaced indifferent directions and by different amounts throughout the assembly510. Such an arrangement allows for assembly 510 to have an array thatis configured differently on the level of surface 544 compared to on thelevel of surface 545. For example, an array can cover a smaller overallarea or have a smaller pitch on surface 544 than at the second surface545 level. Further, some wire bonds 532 can have ends 536 that arepositioned above microelectronic element 522 to accommodate a stackedarrangement of packaged microelectronic elements of different sizes. Inanother embodiment, wire bonds can achieve this lateral displacement byincluding curved portions therein. Such curved portions can be formed inan additional step during the wire bond formation process and can occur,for example, while the wire portion is being drawn out to the desiredlength. This step can be carried out using available wire-bondingequipment, which can include the use of a single machine. Such curvedportions can take on a variety of shapes, as needed, to achieve thedesired positions of the ends of the wire bonds. For example, curvedportions can be formed as S-curves of various shapes.

FIGS. 1-8 show a microelectronic package 10 in various steps of afabrication method thereof. FIGS. 1 and 2 show microelectronic package10 at a step where microelectronic element 22 has been bonded to astructure comprising a patternable metallic element 28′. The structuremay include or consist of a metallic or other electrically conductivematerial layer extending in first and second transverse directions 15,17 to define a general shape of package 10, as can be seen in the planview of FIG. 1. Microelectronic element 22 can be assembled, e.g.,bonded, to the conductive material layer 28′ using an adhesive layer orpolymeric material which is not fully cured. In some embodiments, thestructure may include a support layer or device, e.g., a carrier tosupport the conductive material layer 28′ during at least some stepsduring fabrication. Such a support layer can be removed after formationof the encapsulation layer 42.

FIGS. 3, 4 and 5 show microelectronic package 10 having wire bonds 32joined at predetermined locations on surface 30′ of conductive materiallayer 28′. As discussed, wire bonds 32 can be applied by heating an endof a wire segment to soften the end such that it forms a deposition bondto conductive element 28 when pressed thereto, forming base 34. The wireis then drawn out away from conductive element 28 and manipulated, ifdesired, in a specified shape before being severed to form end 36 andend surface 38 of wire bond 32. Alternatively, wire bonds 32 can beformed from, for example, an aluminum wire by wedge bonding. Wedgebonding is formed by heating a portion of the wire adjacent the endthereof and dragging it along the conductive element 28 with pressureapplied thereto. Such a process is described further in U.S. Pat. No.7,391,121, the disclosure of which is hereby incorporated by referenceherein in its entirety, and in previously-referenced U.S. patentapplication Ser. No. 13/402,158.

In FIGS. 6-8 encapsulation layer 42 has been added to microelectronicpackage 10 by being applied over surface 30′ of conductive materiallayer 28′, extending upwardly therefrom and along edge surfaces 37 ofwire bonds 32. Encapsulation layer 42 can also extend along at least aportion of microelectronic element 22, including over at least one ofthe front face, rear face, or edge surface thereof. In other examples,the encapsulation layer 42 can be formed such that it does not contactany portions of microelectronic element 22, such as by being laterallyspaced away therefrom. Encapsulation layer 42 can be formed bydepositing an encapsulant, e.g., a resin over the stage ofmicroelectronic package 10 shown in FIG. 4. In one example, this can bedone by placing package 10 in an appropriately configured mold having acavity in the desired shape of the encapsulation layer 42 that canreceive package 10. Such a mold and the method of forming anencapsulation layer therewith can be as shown and described in U.S. Pat.App. Pub. No 2010/0232129, the disclosure of which is incorporated byreference herein it its entirety. Alternatively, encapsulation layer 42can be prefabricated to the desired shape from an at least partiallycompliant material. In this configuration, compliant properties of thedielectric material allow encapsulation layer 42 to be pressed intoposition over wire bonds 32 and microelectronic element 22. In such astep, wire bonds 32 penetrate into the compliant material formingrespective holes therein, along which encapsulation layer 42 contactsedge surfaces 37. Further, microelectronic element 22 may deform thecompliant material so that it can be received therein. The compliantdielectric material can be compressed to expose end surfaces 38 on outersurface 44. Alternatively, any excess compliant dielectric material canbe removed from encapsulation layer to form a surface 44 on which endsurfaces 38 of wire bonds 32 are uncovered.

In an example, the encapsulation layer 42 can be formed such that,initially, surface 44 thereof is spaced above end surfaces 38 of wirebonds 32. To expose the end surfaces 38, the portion of encapsulationlayer 42 that is above end surfaces 38 can be removed, exposing a newsurface 44 that is substantially flush with end surfaces 38, as shown inFIG. 7. In a further alternative, encapsulation layer 42 can be formedsuch that surface 44 is already substantially flush with end surfaces 38or such that surface 44 is positioned below end surfaces 38. Removal, ifnecessary, of a portion of encapsulation layer 42 can be achieved bygrinding, dry etching, laser etching, wet etching, lapping, or the like.If desired, a portion of the ends 36 of wire bonds 32 can also beremoved in the same, or an additional, step to achieve substantiallyplanar end surface 38 that are substantially flush with surface 44. In aparticular example, the encapsulation can be applied over themicroelectronic element 22, wire bonds 34, and patternable conductiveelement 28′ without using a mold and excess encapsulant can be removedafter the application thereof to expose the end surfaces of the wirebonds, e.g., by polishing or one or more of the above methods.

After formation of dielectric layer 42, conductive material layer 28′can be patterned, by chemical or mechanical etching (such as laseretching or the like), to make conductive elements 28 and/or traces 31 byremoving portions of conductive material layer 28′ and leaving theportions thereof in the desired locations and form of the desiredconductive elements 28 or traces 31. This can be done to make selectiveinterconnections between wire bonds 32 and contacts 24 ofmicroelectronic element 22 or to form conductive elements 28 displacedfrom respective wire bonds 32 with which they can be connected by traces31. In some embodiments, conductive vias 25 can be formed to connecttraces 31 or conductive features 28 in the form of pads with themicroelectronic contacts 24.

As shown in FIG. 11, the package 10 can then be thinned to planarizesurface 44 and end surfaces 38 of wire bonds 32. This can includeexposing a surface of microelectronic element 22 on surface 44, whichcan also include thinning of microelectronic element 22 itself.Additionally or alternatively, conductive features 28 and/or traces 31can be formed over surface 44, as described above. This can be done bydepositing or joining a conductive layer over surface 44 and thenpatterning the layer to form such conductive elements 28 and traces 31.

FIGS. 16 and 17 show a microelectronic package 110 that is similar inconstruction to that shown in FIG. 10 but with microelectronic element122 in a “face-up” arrangement. In such an arrangement, microelectroniccontacts 124 are disposed toward surface 144 of encapsulation layer 142.Further, microelectronic element 122 can connect with the pattern ofwire bonds 132 by conductive features 128 and traces 131 that areexposed at surface 144. As shown in FIGS. 16 and 17, such traces 131 andconductive elements 128 can connect with microelectronic contacts 124 bymetalized vias 125 that extend from surface 144 to the contacts 124.

As illustrated in FIG. 16, the routing achieved by traces 131 andconductive elements 128 exposed on surface 144 can be the only routingin package 110, with surface 145 being ground down to remove conductivematerial layer 128′ (FIG. 15), which can also remove furtherencapsulation material, bases 134, and all or a portion of theattachment layer 120. Alternatively, as shown in FIG. 16 electricallyconductive routing elements can also be included on surface 145 that canbe for purposes or redistribution of wettable contacts in the array oversurface 145. In other examples, a designated wire bond can connect withthe microelectronic element 122 by routing over surface 144, which can,in turn connect with other wire bonds by routing over surface 145 thatis connected with such designated wire bonds.

FIGS. 14 and 15 show microelectronic package 110 in process steps thatcan lead to either of the completed packages 110 shown in FIGS. 16 and17. Specifically, FIGS. 14 and 15 show package 110 with microelectronicelement 122 bonded, face-up, on conductive material layer 128′.Similarly, wire bonds 132 have been joined to surface 130′ of conductivematerial layer 128′ and formed according to any one of the processesdescribed above. Further, encapsulation layer 142 has been depositedover exposed portions of surface 130′ and over wire bonds 132 andmicroelectronic element 122, according to any of the various processesdescribed above. Routing circuitry in the form of conductive elements128 and traces 131 were then formed over surface 144 of encapsulationlayer 142 to connect wire bonds 132 with microelectronic element 122.

At such a point, package 110 can be further processed by grinding,polishing, lapping or other techniques as described above to removematerial to result in the package 110 shown in FIG. 16. Alternatively,additional routing can be formed by patterning conductive material layer128′ to form conductive elements 128 and traces 131 in the desiredconfiguration, as described above with respect to FIGS. 9 and 10.

FIGS. 18-22 show various arrangements of packages of a similar generalstructure to those described above but utilizing multiplemicroelectronic elements. In one example, FIGS. 18 and 19 show amicroelectronic package 210 having one microelectronic element 222Aembedded within encapsulation layer 242 in a face-down arrangement andanother microelectronic element 222B in a face-up arrangement. Such apackage 210 can utilize electrically conductive routing circuitry in theform of interconnected conductive elements 228 and traces 231 over bothsurface 244 and surface 245 of encapsulation layer 242. Additionally,designated wire bonds 232 can be used to electrically connectmicroelectronic element 222A with microelectronic element 222B byrouting circuitry that connects with such a designated wire bond overeach end surface 35 and 38 and respectively to at least one contact 224of each of microelectronic elements 222A and 222B. Such a package 210can be made by a method that is similar to those described above withrespect to FIGS. 1-16.

FIGS. 20 and 21 show an arrangement of a microelectronic package 310that is similar to that shown in FIGS. 18 and 19, but with an additionalmicroelectronic element 322C in a face-up arrangement bonded over face326 of microelectronic element 322B. To facilitate connection ofmicroelectronic element 322B to electrically conductive routingcircuitry over surface 344, microelectronic element 322C can be smallerthan microelectronic element 322B or can be offset therefrom such thatcontacts 324 of microelectronic element 322B are uncovered bymicroelectronic element 322C. Such a connection can be achieved bymetalized vias 325 that connect with the element contacts 324 or byadditional wire bonds 362 that are joined to contacts 324 ofmicroelectronic element 322B and are uncovered by encapsulation layer342 on surface 344. As discussed above, routing between any of themicroelectronic element 322A, 322B, and 322C can be achieved bydesignated wire bonds 332 with appropriately configured routingcircuitry connected therewith.

In a further example shown in FIG. 22, a microelectronic package can besimilar to that shown in FIGS. 18 and 19, but with additional wire bonds466 that connect between one or more contacts 424 of microelectronicelement 422B (which are disposed toward surface 444 of encapsulationlayer 442) and a portion of the routing circuitry over surface 445 ofencapsulation layer 442. In the example shown, such a wire bond 466 canbe used to achieve a connection between microelectronic element 422B andmicroelectronic element 422A, which has contacts 424 disposed towardsurface 445 of encapsulation layer 442. As shown wire bond 466, or 462,can join with a trace 431 (or a conductive element, if desired) that isfurther connected to a metalized via 425 that electrically connects withelement contacts 424 of microelectronic element 422A, or 422B.

The structures discussed above can be utilized in construction ofdiverse electronic systems. For example, a system 611 in accordance witha further embodiment includes microelectronic package 610, as describedabove, in conjunction with other electronic components 613 and 615. Inthe example depicted, component 613 is a semiconductor chip whereascomponent 615 is a display screen, but any other components can be used.Of course, although only two additional components are depicted in FIG.25 for clarity of illustration, the system may include any number ofsuch components. The microelectronic package 610 as described above maybe, for example, a microelectronic package as discussed above inconnection with FIG. 10, or a structure incorporating pluralmicroelectronic packages as discussed with reference to FIG. 24. Package610 can further include any one of the embodiments described in FIGS.13-23. In a further variant, multiple variations may be provided, andany number of such structures may be used.

Microelectronic package 610 and components 613 and 615 are mounted in acommon housing 619, schematically depicted in broken lines, and areelectrically interconnected with one another as necessary to form thedesired circuit. In the exemplary system shown, the system includes acircuit panel 617 such as a flexible printed circuit board, and thecircuit panel includes numerous conductors 621, of which only one isdepicted in FIG. 25, interconnecting the components with one another.However, this is merely exemplary; any suitable structure for makingelectrical connections can be used.

The housing 619 is depicted as a portable housing of the type usable,for example, in a cellular telephone or personal digital assistant, andscreen 615 is exposed at the surface of the housing. Wheremicroelectronic package 610 includes a light-sensitive element such asan imaging chip, a lens 811 or other optical device also may be providedfor routing light to the structure. Again, the simplified system shownin FIG. 25 is merely exemplary; other systems, including systemscommonly regarded as fixed structures, such as desktop computers,routers and the like can be made using the structures discussed above.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for making a microelectronic unit, comprising: forming a plurality of wire bonds on a conductive bonding surface of a metallic structure, the wire bonds having bases joined to the conductive bonding surface and end surfaces disposed away from the conductive bonding surface; forming a dielectric layer over at least a portion of the conductive bonding surface and over first portions of the wire bonds, the first portions including the bases thereof having the dielectric layer formed thereover for covering the first portions of the wire bonds, second portions of the wire bonds including the end surfaces thereof not covered by the dielectric layer; and patterning the metallic structure to form conductive elements separated from one another by the dielectric layer for having the bases of the wire bonds disposed on the conductive elements.
 2. The method of claim 1, wherein at least some of the wire bonds are formed with the end surfaces thereof displaced in one or more lateral directions away from the bases thereof.
 3. The method of claim 1, wherein: the bases are in a first pattern having a first minimum pitch; and the second portions of the wire bonds are in a second pattern having a second minimum pitch greater than the first minimum pitch.
 4. The method of claim 1, wherein: the bases are in a first pattern having a first minimum pitch; and the second portions of the wire bonds are in a second pattern having a second minimum pitch less than the first minimum pitch. 